Herpes labialis is a recurrent infection of the lip caused most comonly by the herpes simplex virus type 1 (HSV-1). These lesions are frequently referred to as "fever blisters or cold sores". Most people experience their primary infection with HSV-1 as a child. After the initial infection the virus becomes latent or hidden in a nerve without causing any symptoms. When the virus becomes reactivated (often in response to increased exposure to sunlight) it travels down the nerve causing a new outbreak of fever blisters. Approximately 20-45% of people in the United States experience fever blisters. Twenty-five percent of those afflicted report recurrent outbreaks in excess of 3 per year. There is currently not an oral drug approved for the episodic treatment of recurrent herpes labialis, although acyclovir and famciclovir have shown some benefit in reducing the time to healing. Lobucavir has been shown to have a broad spectrum of antiviral activity in vitro. Although the mechanism is unclear, it does inhibit HSV replication in infected cells. It has also been shown to be effective in a variety of HSV infected animal models. The safety and efficacy of Lobucavir is being evaluated in herpes labialis in this protocol.